What did Sternberg and Detterman (1986) say that psychological definitions include?
- Higher level abilities
- Valued by culture
- Executive processes
Intelligence comprises the “mental abilities necessary for adaptation to, as well as shaping and selection, of any environmental context (Sternberg, 1997)
What is the IQ test?
- Usually assess IQ which is standardised to a mean score of 100 and SD of 15
- Norming involves administering IQ test to a representative sample of a population to obtain norms or referential scores for different sub-groups
What did Deary and Caryl (1997) say about neuroscience and human intelligence?
Individual differences > real life impacts/ structure of intelligence/ biological
Individual differences > cognitive > biological
Individual differences > biological
What is fluid intelligence (Gf) according to Horn and Cattel (1966)?
“a capacity to perceive relationships independently of previous specific practice or instruction related to those relationships”
- Process independent of content or knowledge domain
- Includes executive control and working memory tasks
- Biologically instantiated in the pre-frontal cortex - declines later in life
What is crystalised intelligence? (Gc)
- Gc test: vocabulary etc represent acquired knowledge
- Gc is a product of Gf
- Investment theory – investment of fluid intelligence in a specific body of knowledge
- Knowledge increases over lifetime
What do Gc and Gf look like over the lifetime?
Conventional wisdom is that fluid intelligence peaks relatively early in life and then declines
Challenged by more current research suggesting heterogenous effects on different cognition domains
What are behavioural genetics?
- Heritability estimates for IQ range from 0.42 to 0.62
- Between 48% and potentially up to 80% of the variability in IQ scores is attributed to genetic variation
- Mind the heritability gap (Plomin & Deary, 2015)
- gap between estimated heritability of intelligence and amount of variability we can attribute to genes
What are group differences controversies within heritability of g?
- Behavioural genetics assumes independence of genes and environment
- Fluid intelligence is fixed and crystallised intelligence less so
- Heritability within groups tells us nothing about the causes of differences between groups
What is the Spearman’s hypothesis?
- Performance on a cognitive test correlated with their performance on other comparable cognitive tests
- More strongly a test correlated with IQ, the wider the difference in Black and White Americans’ performance on the test
- Hypothesised that Black-White differences on tests of cognitive ability correlate positively with a test’s*g-loading
- Extended by other authors to suggest that racial IQ differences are genetic in origin
What did Fagan and Holland (2002,2007) say about evidence about racial group differences in IQ?
- No performance differences between Black and White Americans given equal prior exposure to test-relevant information
- Group differences reflect unequal opportunity to acquire information, not differences in cognitive processing capacity
What did Nisbett et al (2012) say about evidence about racial group differences in IQ?
- A review by 16 intelligence researchers - Evidence for a genetic basis for group differences is weak, and that environmental factors are sufficient to account for observed gaps
What did Bird (2021) say about genome-wide evidence?
- Large scale polygenic analyses find no evidence that intelligence was under divergent selection across ancestral populations
- genetic differences between racial groups are not a meaningful driver of IQ gaps
What is the Flynn effect?
- Generation rise in IQ by average of 10 percentage points
- Seen across at least 14 countries
- More substantial for Gf than Gc
- Stronger among adults than children
- Highest in the Netherlands, below average in the UK, ceased in Sweden and reversed in Norway
What is the heritability paradox?
- Social multipliers
- Averaging
- Gene-environment matching
What are social multipliers?
Environmental factors potentially contributing to an increase in IQ
- Internet and access to information
- Education
- Rising standards of living
- Better nutrition
What is averaging?
- As individuals’ ability rises, this will also influence those around them.
- Small effects over time will influence the population more widely
- The population average will increase
What is genome-environment matching?
- Gene-environment correlation - people seek out environments that match their phenotype
- Process by which the ability and the environment are matched produces increases in that initial ability
- Thus, environment increases biological ability
What are environmental toxins?
- US Americans born in the 60s lost up to six IQ points on average due to lead exposure (McFarland et al., 2022)
- Removal of lead from petrol was followed by measurable population-level IQ increases across multiple countries (Reyes, 2007)
What did Turkheimer et al (2003) say about gene-environment interaction in heritability of IQ?
Genetic primacy is a phenomenon of relative privilege
Genes can only express potential once basic environmental conditions are met
Environmental stresses may detract from resources of IQ
How did Bouchard Jr (2013) propose the ‘Wilson effect’?
- Genes need the appropriate environment to express.
- High IQ people will seek out high IQ contexts and as they get older their intelligence will show
- Heritability increases with age
- 40% in childhood, 60% in adulthood and 80% in old age
What did Sauce and Matzel (2017) say about genetically-determined, low heritability traits?
- Heritability of number of human fingers is next to zero
- Main predictors of variance are environmental
What did Sauce and Matzel (2017) say about highly heritable but not genetically determined traits?
- In the US, heritability of voting is 53% and heritability of voting for specific parties is 46%
Due to gene-environment interplay, IQ is more malleable than previously assumed
The most heritable subtests are also the most culturally loaded
G factor itself partly reflects cultural experience and education, not just biological potential (Kan et al., 2013)
What is the heritability of g?
- Hereditarian views on race and intelligence were highly controversial
- Current research has confirmed that IQ is heritable
- No evidence of significant genetic determination of racial differences in IQ
- Group differences in IQ may be entirely explained by environmental factors
What did Ackerman (2018) say about intelligence as a process, personality, interests and knowledge?
Processing > interests > knowledge
Processing > knowledge > personality > interests > knowledge
- over time
- Stage 2: knowledge influences interests and this is mediated by personality
